Potamotherium

Though the following article does detail an official piece of Land Before Time media approved of by Universal, it should in no way be seen as a canon part of the Land Before Time universe established by the movies and TV series episodes.

Potamotherium ("river beast") is an extinct genus of either mustelid or pinniped from the Miocene of Europe and North America. It physically resembled an otter and, just like an otter, it was a skilled swimmer. It had a good sense of hearing and sight but a terrible sense of smell. It is theorized to have been an early ancestor of seals and sea lions. If it is a pinniped and not a mustelid, as it is currently believed to be, it would be a missing link between the early ancestors of seals and sea lions and their modern descendants.